Healthy air humidity (Part 4)

In this technical paper by Nortec, we look at air humidification with steam, reduction of operating costs with indirect evaporative cooling and air humidification technologies.

Air humidification with steam

Hygiene is a top priority in hospitals. Electric steam humidifiers generate an absolutely germ-free atmospheric air humidity, as the water used is heated to temperatures of 100°C, which no germ or disease-causing agent can withstand. For this reason, mineral-free or regular tap water can be used, no special processing is required.

Steam air humidifiers can be integrated into any existing central air conditioning system or, in most cases, retrofitted. They are easy to clean and maintain. For the even injection and distribution of the steam in the air flow, it is especially important to implement the humidification distance correctly.

It is made up of the mist zone and the subsequent expansion and mixing zone. When this is measured properly, the occurrence of condensation inside the air pipes is prevented.

In addition, this prevents water aerosols from reaching the filter. The humidification distance is also important for correct humidity control, since control sensors should only be installed where there are balanced humidity values. Due to the quick and homogeneous mixing with the system supply air, in the case of extensive steam injection, significant reductions of the humidification distance are also achieved.

Image credit: Steam air humidifiers can be integrated into any existing central air conditioning system or, in most cases, retrofitted.>

Reduction of operating costs with indirect evaporative cooling

Indirect evaporative cooling, also known as adiabatic cooling, is a process in which latent and sensitive evaporative heat from water can be used to cool supply air in a hospital’s HVAC system. To do this, the water is firstly evaporated on the exhaust air side of a HVAC system using an evaporative cooler. Heat energy is removed from exhaust air in the process, thus, it cools down. Then the exhaust air is conducted close to the warm external air in the crossflow, without coming in contact with it. From a hygiene point of view, this solution is absolutely harmless, which is very important for hospitals or other medical areas. Through heat recovery from the external air, the added moisture in the exhaust air condenses once again, therefore heating the exhaust air and cooling the supply air at the same time.

Apart from the speed at which air passes through the evaporative cooler, the evaporated water quantity and hence the attained cooling depend on the condition of the output air which enters the evaporative cooler. The theoretical limit of evaporative cooling is reached upon complete saturation of the exhaust air with water, i.e. at a relative humidity of 100 percent. Humidity increases up to values between 92 and 95% are realistic in air conditioning systems at economically viable cost, depending on the design of the evaporative cooler used.

As mentioned previously, indirect evaporative cooling is suitable for the sensitive cooling of the supply air. Depending on the location, on especially hot days or for redundancy reasons, if additional cooling energy is required, a mechanical cooling system can also be used – but this can be a much smaller size. In a suitable system design, much more electrical driving energy for a cooling system is saved by indirect evaporative cooling than is needed to overcome the additional air-side pressure loss through the extractor fan.

Image credit: Indirect evaporative cooling is suitable for the sensitive cooling of the supply air.

The question of cost-effectiveness

In practical terms, the greatest hurdle when using renewable energy is cost-effectiveness. Efficiency measures such as indirect evaporative cooling have to “pay”, additional costs incurred during the investments must be absorbed again through the savings achieved during operation.

A reliable system simulation therefore makes the relationships transparent and allows a realistic comparison with conventional measures for cooling buildings. Since HVAC systems in hospitals work to condition the air all year round and have to meet the highest possible standards for hygiene reasons and for the preservation of health, it has to be considered that in many cases a depreciation will set in within an acceptable time frame. From the operating cost viewpoint, the system thus proves economical right from the first day.

Air humidification technologies

There are various air humidification technologies available, including: